1. Field of the Invention
This invention relates to a method of making propylene. More particularly, this invention relates to the production of propylene, with or without the formation of methyl tertiary butyl ether (MTBE).
2. Description of the Prior Art
From time to time there exists in the world geographical areas or regions (areas), where propylene availability is either non-existent or in limited supply. There can be large areas, for example, Europe at present, where propylene is available, but only in limited supply.
There are other areas in the world where natural gas (gas) is available, but there is no gas pipeline nearby which can be used to transport the gas to market in an economical manner. This type of gas is known as “stranded” or “remote” gas. Natural gas usually contains both ethane and propane, both of which can be separated from the gas in its remote location. This can be done, for example, when forming liquefied natural gas for transportation to market on a natural gas liquids transport ship. Ethane can be converted in known manner into ethylene by a process generally known as pyrolysis or thermal cracking. Ethane cracking to form ethylene is commonly practiced in remote areas and is quite often the low-cost supply of ethylene in the world. On the other hand, propane dehydrogenation to form propylene is expensive and usually the highest cost supply. Further, in remote areas propane has a high value of its own as a cooking and heating fuel. This also dictates against using propane as a feedstock to produce propylene in remote areas.
Thus, ethylene can be economically produced, given a natural gas supply, even in remote areas, while the same is not true for propylene. This invention, by virtue of its use of ethylene, and not propylene, as a feedstock is highly useful anywhere there is a source of natural gas no matter how remote the location of that source, or where excess ethylene is available, such as Europe or North America.
There are yet other areas in the world that either limit or prohibit the use of MTBE in automotive gasoline. In some areas, although there is currently a demand for MTBE, that demand is gradually being reduced for various reasons.
Propylene under supply and MTBE over supply at first may appear to be unrelated problems, but, as will be seen hereinafter, they can be related.
This invention provides a solution for both propylene and MTBE supply problems, whether they be over supply, under supply, or a combination thereof, and does so in a manner that utilizes ethylene as the primary feed. Thus, this invention is useful in remote areas that contain stranded gas as well as other areas of the world that are not remote and have an available ethylene supply and a limited propylene supply.